Amazon's Prime Day has become not only a spending holiday for consumers shopping the marketplace but also a huge opportunity for all retailers across the web. In fact, Criteo data shows that for retailers that started advertising deals and sales early in the week before July 10, 2017, sales were up 30% from normal July activity.

Jaysen Gillespie, VP and head of analytics and data science at Criteo, shared with FierceRetail some of the data captured on last year's Prime Day, along with what retailers should be doing to prepare for this year's summer sales boom.

FierceRetail: What did we learn about consumers from last year's Prime Day?

Jaysen Gillespie: What started out as Amazon’s annual summer discount event has become something much bigger—a new online shopping peak when consumers search for deals and discounts at retailers all across the web. The 2017 peak began on July 10 at 9 p.m. EST and ran for a full 30 hours, causing a surge in sales across the web. Like a warm-weather Black Friday, it presents a huge opportunity for all brands and retailers.

During the 2017 summer peak, brands and retailers saw sales rise by as much as 30% over the course of the week. Mass merchants’ sales grew by 124% on the day itself. And if last year’s sales are any indication, the opportunity to benefit from the quickly approaching 2018 event is only getting bigger.

FierceRetail: Did Prime Day negatively affect any retailers?

Gillespie: Though it may come as a surprise, last year’s Criteo data shows that non-Amazon retailers actually benefit from Amazon Prime Day. Across the U.S., anticipation and excitement about the big event make it an ideal opportunity to take advantage of the elevated purchase intent already on shoppers’ minds. In fact, retailers who ignored Amazon Prime Day saw the lowest bump in sales at more than 5% during the week of the event. Retailers who timed their promotional and marketing activity to align with that of Amazon saw the best performance on Prime Day itself and then generated more than 25% in sales that week.The grand prize went to retailers who anticipated Amazon’s timing and started their promotional activity just ahead of Amazon. These early birds generated more than 30% in sales over the course of the entire week.

FierceRetail: How did the day positively affect other retailers?

Gillespie: The halo effect of Amazon Prime Day is bright. In 2017, there was an average sales increase of more than 57% in top-performing categories, from fashion and health/beauty to home improvement and sporting goods. Mass merchants saw the biggest gains, at more than 124% on Prime Day. Other stats that lit up from coast to coast were 27% add-to-basket rates, 33% average order values, and 41% conversion rates.

FierceRetail: So what should online retailers be doing to prepare for Prime Day 2018?

Gillespie: With site visitor volumes and intent soaring, this peak is a vital time for retailers to maximize the visibility of their brand, heavily promote deals and products, and aggressively pursue high-intent audiences who are converting at rates 41% higher than normal. To reach in-market shoppers across the internet, retailers can target them with relevant ads that bring them back to a preferred retailer’s site. Uncapping frequency will also take advantage of high consumer intent and help brands acquire new customers.

Our data also found that online retailers who anticipate Amazon Prime Day by 24 hours are those who benefit the most. Minimizing discounting the week before the big event—but then starting just before Amazon does—will maximize retailers’ ability to compete with Amazon on and around Prime Day.

FierceRetail: And physical retailers?

Gillespie: As customers are researching deals, discovering new products, and spending more money, brands should keep their offers out in front and top-of-mind. They should plan to start pushing brand awareness with high-funnel placements starting in early July, with the peak expected on or around July 9. Brick-and-mortar retailers should also start leveraging promotional items to attract shoppers and put trade agreements in place with retailers that offer sales and discounting. As with online retailers, minimizing discounting before the big event will also help maximize a physical retailer’s ability to compete with Amazon on Prime Day.

FierceRetail: Your best advice for preparing for the big day?

Gillespie: As our findings detailed, retailers who react to Amazon initiatives will benefit from it. Retailers who anticipate Amazon Prime Day by 24 hours are those who benefit the most. Minimizing discounting before the big event will maximize their ability to compete with Amazon on Prime Day.

Another consideration our studies have shown are continuing shifts from desktop to mobile shopping, as well as from retailer websites to apps. Today’s shopper is on-the-go and researching across multiple screens, requiring a cohesive, data-driven approach to intersect and influence buying decisions. Omnichannel data is key to optimizing marketing efforts; retailers that combine offline and online data can apply over four times as much sales data to inform their marketing strategies.